The use of non-stick coatings is well known in the art. While the prior art discloses a myriad of non-stick coatings and applications for the non-stick coatings, the composition of non-stick coatings varies and each variation brings different considerations, many of which are not useful in the field of high heat welding applications. Innovations for improved non-stick coatings are partly a result of the desire to have a coating that is easily applied, environmentally safe and more effective in prolonging the life of a sensor in a welding environment through increased heat dispersion and non-porosity.
Electromagnetic proximity sensors are employed in automobile assembly lines to detect the position of parts during welding operations conducted by robotic welders. As the sensors are proximate to the hot welding operation, slag from the welding process is splattered onto the sensors. Unless the slag falls off the sensor, the slag accumulates on the sensor and can eventually render the sensor inoperative. When the sensor becomes inoperable, the downtime from the delay needed to replace the sensor is expensive and includes the costs from delayed production as well as the costs associated with repair and replacement parts.
Solutions to the problem of weld slag exist in the art, such as alternate construction materials and specialized protective accessories. U.S. Pat. No. 6,617,845 by Shafiyan-Rad, et al., entitled “Proximity sensor resistant to environmental effects,” claims a special housing for a proximity sensor that is made of a material with high thermal conductivity, such as copper or an alloy thereof. This device uses the inherent properties of the housing material to disperse heat and does not involve applying any coating.
Non-stick polytetrafluoroethylene (or PTFE) coatings, such as Teflon® (registered trademark of DuPont), are currently being used to reduce the impact of weld slag. However, over time the weld slag particles abrade the PTFE coatings and pits start to develop in the surface of the coating. This pitting or porosity is problematic in that even the smallest pits or pores provide a means by which weld slag can adhere to the coating. Over time, the weld slag accumulates until the sensor is rendered inoperable, requiring the replacement of the sensor. Even in the case of non-porous polyfluorocarbon based coatings, there are surface imperfections to which the weld slag attaches to form a layer that subsequently causes the sensor to stop functioning. The current state-of-the-art PTFE coatings fail after approximately 2500-3500 welding operations. U.S. Pat. No. 4,996,408 by Turck, et al., entitled “Proximity switch for use in welding facilities,” claims a non-stick coating applied to proximity switches where the coating is polytetrafluoroethylene (or PTFE) with perfluoroalkoxy side chains. This application used PTFE as a non-stick coating but does not involve mixing the PTFE with any additional materials, other than coloring pigments, to form a special coating. Further, many coatings currently available tend to be non-aqueous based, which makes manufacturing them expensive since the manufacture has to be compliant with volatile organic carbon (VOC) emission standards.